Produce production in North America is a multi-billion dollar industry. Consequently, improving and preserving the quality of fruits, vegetables and other types of produce in terms of their colour, taste, flavour and storage-life are of paramount importance to growers, produce-processing companies and the food industry in general. Unfortunately, the time window where most fruits, vegetables and produce exhibit peak quality is relatively narrow, and after this time window, the quality of the produce tends to decrease rapidly.
Superficial scald (or scald) is a physiological disorder that affects certain varieties of apples during or after post-harvest storage, lowering their market value several-fold. Varieties affected include Red Delicious, McIntosh, Cortland, Granny Smith and others. Collectively, these varieties comprise over 60% of the apples produced in Canada and the United States. In addition to affecting apples, superficial scald may also affect certain varieties of pears.
Superficial scald is primarily characterized by damage to the surface of fruit. Often, scald manifests as patchy browning on the surface of the fruit. This symptom can progress to internal damage and contribute to other pathological disorders. Superficial scald development in apples and pears is a form of targeted senescence, where the hypodermal cell layers (3–4 cell layers beneath the cuticle) undergo damage and deterioration. At present, the cause of superficial scald is unknown, but specific plant metabolic pathways have been implicated in its development. Also, environmental conditions such as hot dry weather, nutrient availability, and lack of appropriate chilling conditions during ripening may contribute to the development of superficial scald (Blanpeid et al., 1991; Patterson and Workman 1962).
One theory regarding the mechanism of scald development proposes that the component a-farnescene, present in the superficial cell layers of fruit undergoes peroxidation through an as yet unknown mechanism and the peroxidized products somehow cause tissue damage and browning (Anet and Coggiola, 1974). Supporting the contention that free radicals may be involved in the development of the disorder, application of antioxidants such as a-tocopherol to scald-sensitive fruits can negate the development of superficial scald (Barden and Bramlage, 1994).
Scald development may be inhibited by treating scald-susceptible apples with diphenylamine (DPA) or ethoxyquin. However, some apples such as “Golden Delicious” can develop a blue-grey discoloration on the cheeks and shoulders of the fruit after DPA treatment (Pierson and Schomer, 1968). Further, although DPA and ethoxyquin application inhibit scald development in many varieties of apples, these chemicals may be degraded into compounds which can include potential carcinogens. This has resulted in banning DPA and ethoxyquin application to fruit in several European countries.
Other biochemical pathways have also been implicated in the mechanism of scald development in apples, and the deterioration of produce other than apples. For example, it has been suggested that membrane deterioration during senescence and stress may involve the action of phospholipase D. Phospholipase D (PLD) is a ubiquitous enzyme that catalyses the hydrolysis of membrane phospholipids. However, it has also been proposed that normal maturation and ripening of many types of fruits and vegetables may be due to catabolic breakdown of cellular structures such as the membrane and the cell wall, and that phospholipase D may be directly involved in this process. Also, untimely destruction of cellular integrity of the produce, as often occurs during processing (cutting, wounding, blending, etc) or storage (injury due to chilling) can lead to accelerated destruction of cellular structures, resulting in a loss of quality of the intended product.
There has been much research into compositions that may replace diphenylamine to inhibit scald development in apples, as well as compositions which may be effective in enhancing or extending the food-quality of other produce such as fruits and vegetables.
U.S. Pat. No. 6,054,160 discloses complex compositions and processes for treating fresh-cut apple pieces, as a replacement for sulfite treatment. The composition consists of an antioxidant or reducing component such as cysteine, an osmolite such as sorbitol and a membrane integrity-enhancing agent such as calcium chloride. A chelator such as sodium hexametaphosphate can be added to enhance the affiance of the agent. The compositions are administered by dipping the pieces in an aqueous solution which protect the pieces from deterioration due to increased enzymatic activity, oxidative reactions, water migration and microbes. While the composition may enhance the fresh sensory attributes of freshly cut apples, the composition may not be applied to apples pre-harvest. Furthermore, there is no disclosure as to whether the compositions have any effect on scald, or whether the compositions are effective in enhancing the food quality of other fruits and vegetables.
U.S. Pat. No. 5,858,436 discloses an aqueous treatment composition comprising a polyphenol-type antioxidant alone or in combination with a terpenic compound in an aqueous vehicle for treatment of fruits or vegetables after harvesting. The composition must be heated to a temperature of 40–60° C. and subsequently the fruits or vegetables are brought into contact with the liquid treatment composition at the elevated temperature for a period of less than or equal to 10 minutes. The composition is not suitable for spraying onto fruits and vegetables and the composition must be applied post-harvest.
U.S. Pat. No. 5,376,391 and U.S. Pat. No. 5,198,254 disclose coating compositions which may increase stability of fruits, vegetables or fungi. The compositions comprise at least one polysaccharide polymer, a preservative and an acidulant. The compositions may also include at least one emulsifier, a plasticizer, a resin or rosin, a protein, a firming or sequestering agent, an antioxidant and a plant growth regulator and a chilling injury protectant. It is suggested in the patents that the coatings of the invention may act as a partial barrier to water vapour, oxygen, carbon dioxide and possibly flavour volatiles, thereby causing an alteration in metabolic processes within fruit. No specific metabolic processes or pathways are preferentially inhibited by these compositions, and they may inhibit both beneficial and detrimental metabolic processes within fruits. Moreover, some of the compositions contemplated comprise components which are not normally associated with fruits, vegetables and fungi, or that are normally found in such produce in much lesser quantities. The inclusion of many non-natural components may be undesirable to the consumer. Also, it is unknown whether the disclosed compositions may inhibit superficial scald-development in apples and pears.
U.S. Pat. No. 5,126,155 teaches the use of lysophosphatidylethanolamine for the treatment of pre harvest and post harvest applications.
U.S. Pat. No. 4,988,522 provides compositions useful in the treatment of cut plant parts to improve their quality and storage stability against the effects of oxidation, thermo-oxidation, enzymatic, microbial and metal ion attack. The compositions include an antioxidant, an enzyme inhibitor, an acidulant and a unique metal ion sequestrant which is compatible with the acidulant. Further, the patent teaches that the antioxidant may comprise ascorbic acid and that a chloride ion source may be included. The food preservative compositions disclosed are limited to dips and to treating cut surfaces of edible plant parts. There is no disclosure whether the compositions may be useful for the treatment of superficial scald and other disorders of unprocessed produce.
U.S. Pat. No. 3,526,520 discloses treating and controlling apple storage scald with compostitions comprising diphenylamine, an emulsifier, and an organic solvent. Diphenylamine is a material which may be degraded into potentially toxic compounds. Thus, it is preferable that novel compositions be developed which circumvent the use of diphenylamine to control scald in apples and other fruit.
WO 91/05479 teaches of a preparation for treating apples, pears, and other vegetables to protect them against scald and cold damage. The composition comprises an aqueous solution of sucrose ester(s) and at least one antioxidant selected from natural and synthetic agents including tocopherols, ascorbic acid, esters of gallic acid, vitamin E, butylated hydroxy toluene (BHT), butylated hydroxyanisole (BHA), and 6-O-palmitoyl-L-ascorbic acid. A drawback to the disclosed compositions is that they employ antioxidants which are nonspecific in their functioning as opposed to employing compounds which may directly inhibit specific metabolic pathways that are activated as a result of scald development or cold damage. Furthermore, the application must be done post harvest.
The post-harvest fumigation of apples with ethanol and longer chain alcohols such as hexanol has shown that higher alcohols are less effective than ethanol in controlling superficial scald (Ghahramani et al, 1999).
There is a need in the art for compositions that are generally regarded as safe (GRAS) and that are capable of inhibiting superficial scald in apples and pears and preserving other produce such as, but not limited to fruits, vegetables and portions thereof. Moreover, there is a need in the art for compositions which preserve fruits, vegetables, other produce and flowers, wherein the composition may be applied by spray, drench or by dip. Also, there is a need in the art for compositions which may be used to preserve unprocessed, partially processed or fully processed produce. Further, there is a need in the art for compositions that may be applied either preharvest, or post harvest, for the preservation of fruits, vegetables, other produce and flowers, wherein the compositions comprise components which inhibit specific metabolic pathways and thus provide both targeted and preventative damage control.
It is an object of the present invention to overcome drawbacks in the prior art.
The above object is met by a combination of the features of the main claims. The sub claims disclose further advantageous embodiments of the invention.